1. Field of the Invention
The invention relates generally to X-ray sensor arrays which comprise a plurality of sensor elements forming the arrays. More specifically, the invention relates to a novel method and circuit arrangement for measuring the intensity of the light falling on the sensor elements. The invention also relates to a novel and advantageous configuration of sensor elements for forming such a sensor array.
2. Description of Prior Art
Sensor arrays for X-ray detection or other uses are already known in the art. For example, U.S. Pat. No. 4,064,440, Roder, Dec. 20, 1977, U.S. Pat. No. 4,430,563, Yoshida et al, Feb. 7, 1984, U.S. Pat. No. 4,426,721 Wang, Jan. 17, 1984, U.S. Pat. No. 4,535,243, Peschmann, Aug. 13, 1985, U.S. Pat. No. Re. 32,164, Kruger, May 27, 1986, U.S. Pat. No. 4,153,839, Hounsfield et al, May 8, 1979, U.S. Pat. No. 3,937,965, Vasseur, Feb. 10, 1976 and U.S. Pat. No. 4,075,492, Boyd et al, Feb. 21, 1978, teach linear arrays of photosensitive elements.
U.S. Pat. No. 4,181,856, Bone, Jan. 1, 1980, teaches a sensor array comprising scintillator crystals and photodiodes which are mounted in assemblies of sub-arrays of, for example, four units. The mountings are shaped to permit a complete assembly in the form of a ring.
U.S. Pat. No. 4,542,519, Sugimoto, Sep. 17, 1985, teaches a sensor array comprising alernating scintillation crystals and photoelectric transducers optically coupled. The outputs of the photoelectric transducers are fed to integrating amplifiers.
U.S. Pat. No. 4,504,962 teaches a switching arrangement for combining the outputs of two, four, eight . . . adjacent detectors, or for using the outputs of each detector individually. The output of each sensor in a sensor array as taught in U.S. Pat. No. 4,583,240, Gatten et al, Apr. 15, 1986 is fed to a track and hold circuit arrangement which includes a voltage follower transistor and resistor, a Butterworth filter, a transconductance amplifier including a charging capacitor, and an analog-to-digital converter.
In U.S. Pat. No. 4,484,340, Yamaguchi et al, Nov. 20, 1984, the output of sensors I.sub.1, I.sub.2 . . . I.sub.n are fed, one at a time, to amplifier U through switches S.sub.1, S.sub.2 . . . S.sub.n respectively. Reset switch, S.sub.r, across the input of amplifier U, discharges distributed capacitance C.sub.x across the input of the amplifier.
U.S. Pat. No. 4,366,382, Kotowski, Dec. 28, 1982, teaches a linear array of photodetectors. To measure the intensity of light falling on the photodetectors, a separate integrating amplifier is required for each photodetector. Canadian Patent 1,090,482, Beland, Nov. 25, 1980, teaches a linear array of phototransistors as sensor elements for sensing the light intensity falling on the phototransistors. As explained with respect to FIGS. 4A, 4B and 4C of the patent, the intensity of the light falling on the phototransistor is measured by measuring charging current. Both the '382 patent and the '482 patent teach linear arrays of sensors.
In the prior art, the measurement methods and circuits for measuring the intensity of light falling on the sensors is typically complex and requires a large number of parts. Accordingly, the reliability of the measurement circuit is necessarily low. For example, in the '382 patent, a separate amplifier is required for each sensor.
In addition, except for the '490 patent, the prior art does no address itself to the question of density of sensors in an array. Obviously, the greater the density, the better will be the image detected by the array.